This invention is concerned with providing a fuze in a solid electrolyte capacitor and relates to an improvement to the methods and the capacitors described in commonly assigned U.S. Pat. No. 4,899,258 issued Feb. 6, 1990 and U.S. application Ser. No. 07/474,572 filed Feb. 2, 1990.
A solid electrolyte capacitor, especially one of the tantalum type, essentially comprises a porous anode from which projects an anode wire. The porous anode is completely or partly covered with various layers: in practice these layers are of dielectric/oxide and of manganese dioxide substantially filling the pores of the anode and constituting the solid electrolyte, and a conductive layer forming the cathode. This structure constitutes a capacitor body which is covered with an electrically insulative material after fixing the electrodes to connecting tangs which terminate in output leads. The capacitors obtained in this way are very compact with simple geometrical shapes of cylindrical or more usually rectangular parallelepiped-shape.
With the aim among other things of reducing the unfortunate consequences of a short-circuit in a circuit comprising one or more solid electrolyte capacitors attempts have been made to integrate a fuze into the capacitor with minimum increase to its overall dimensions.
Various types of capacitors with integral fuzes are already known. Examples can be found in the documents U.S. Pat. No. 4,107,762; U.S. Pat. No. 4,224,656; EP 0,232,868; and FR 2,633,770.
The documents U.S. Pat. No. 4,224,656 and EP 0,232,868 determine the effective length of the fuze wire using an additional support member apparently needed during manufacture to hold the areas to which the ends of the fuze wire must be attached a predetermined distance apart.
The object of the previously mentioned U.S. Pat. No. 4,899,258 is to simplify further the integration of a fuze into a solid electrolyte capacitor and therefore to reduce its cost, while achieving a comparable level of performance, by eliminating any intermediate support member disposed between the negative connecting tang and the other electrode. It proposes, to this end, the provision of a predetermined effective length of calibrated fuze wire between two electrically isolated sections of the tang, which is directly connected by one of its sections to the other electrode.
The various solutions described above share the disadvantage of having no easy way to check the integrity of the fuze because it is in series with the capacitor proper, as this is essential for it to fulfil its function.
The previously mentioned patent application Ser. No. 07/474,572 is directed to meeting the object of U.S. Pat. No. 4,899,258 by additionally providing an easy way to check the integrity of the fuze by providing a solid electrolyte capacitor body fitted with two electrodes respectively connected to two connection tangs constituting the (+,-) output leads, a fuzible member of predetermined length being mounted in series between the capacitor body and a selected (-) output lead, such that the connecting tang incorporating the selected output lead is formed by a first section fixed to one of the electrodes to form a test lead and a second section electrically isolated from the first section and from the capacitor body to form the selected (-) output lead, the fuzible member providing the only electrical connection between these sections and being surrounded with a rigid or flexible and thermally insulative supporting mass of resin extending between the two sections.